PHOENIX (AP) — Federal police have arrested two men who may be connected with the fatal shooting of a U.S. Border Patrol agent just north of the Mexico-Arizona border, a Mexican law enforcement official said Thursday.

The official, who spoke on condition of anonymity because he was not authorized to release the information, said it was unclear if there was strong evidence linking the men to the shooting of Agent Nicholas Ivie.

Ivie and two other agents were fired upon Tuesday in a rugged hilly area about five miles (eight kilometers) north of the border near Bisbee, Ariz., as they responded to an alarm that was triggered on one of the sensors that the government has installed along the border.

The wounded agent was shot in the ankle and buttocks and released from the hospital after undergoing surgery. The third agent wasn’t injured.

Brenda Nath, an FBI spokeswoman in Arizona, and Border Patrol officials in Arizona declined to comment on the detention of the two men in Mexico. The Cochise County sheriff’s office, which is also investigating the shooting, didn’t immediately respond to requests for comment.

Lydia Antonio, a spokeswoman for the Mexican Embassy in Washington, confirmed the two detentions, but declined to say what prompted them and what made authorities suspect the two might be involved in the shooting.

At a news conference Thursday in Washington, Attorney General Eric Holder said he is getting updates on the investigation’s progress and has spoken with Homeland Security Secretary Janet Napolitano about the probe.

Napolitano is traveling to Arizona on Friday to express her condolences to Ivie’s family and to meet with law enforcement authorities in southern Arizona about the investigation.

Authorities have declined to provide key details about Tuesday’s shooting, including what they believe prompted the shooting, whether the agents were ambushed and whether any guns from the shooting were recovered. Still, they suspect that more than one person fired on the agents.

The head of the Border Patrol agents union has said he believes those who carried out the shooting probably had time to escape in the early morning darkness before authorities could seal off the area and that he doubted that whoever shot the agents would still be hiding in the area.

In nearby Sierra Vista, Ariz., family members described Ivie as a devoted Mormon who developed a love for the country’s people and culture while serving on a mission in Mexico City.

Ivie’s brother, Chris Ivie, remembered that his brother came across a pregnant woman one time while on patrol who had lost her shoes and had her feet cut up. “He carried that woman a mile and a half to where she could receive the proper help that she needed,” Chris Ivie said.

Ivie’s death marked the first fatal shooting of an agent since a deadly 2010 firefight with Mexican bandits that killed U.S. Border Patrol Agent Brian Terry in December 2010 and spawned congressional probes of a botched government gun-smuggling investigation.

Terry’s shooting was later linked to that “Fast and Furious” operation, which allowed people suspected of illegally buying guns for others to walk away from gun shops with weapons, rather than be arrested.

Authorities intended to track the guns into Mexico. Two rifles found at the scene of Terry’s shooting were bought by a member of the gun-smuggling ring being investigated. Critics of the operation say any shooting along the border now will raise the specter that those illegal weapons are still being used.

Twenty-six Border Patrol agents have died in the line of duty since 2002.